Clin Oral Invest (2013) 17:725–729
DOI 10.1007/s00784-012-0753-x
ORIGINAL ARTICLE
Visual acuity of dentists under simulated clinical conditions
Martina Eichenberger & Philippe Perrin &
Klaus W. Neuhaus & Ueli Bringolf & Adrian Lussi
Received: 4 January 2012 / Accepted: 14 May 2012 / Published online: 26 May 2012
# Springer-Verlag 2012
Abstract
Objectives This study examined the near visual acuity of
dentists in relation to age and magnification under simulated
clinical conditions.
Materials and methods Miniaturized visual tests were performed in posterior teeth of a dental phantom head in a
simulated clinical setting (dental chair, operating lamp, dental mirror). The visual acuity of 40 dentists was measured
under the following conditions: (1) natural visual acuity,
distance of 300 mm; (2) natural visual acuity, free choice
of distance; (3) Galilean loupes, magnification of ×2.5; (4)
Keplerian loupes, ×4.3; (5) operating microscope, ×4, integrated light; (6) operating microscope, ×6.4, integrated
light.
Results The visual acuity varied widely between individuals
and was significantly lower in the group ≥40 years of age (p<
0.001). Significant differences were found between all tested
conditions (p<0.01). Furthermore, a correlation between visual acuity and age was found for all conditions. The performance with the microscope was better than with loupes even
with comparable magnification factors. Some dentists had a
better visual acuity without optical aids than others with
Galilean loupes.
Conclusions Near visual acuity under simulated clinical
conditions varies widely between individuals and decreases
M. Eichenberger : P. Perrin (*) : K. W. Neuhaus : A. Lussi
Department of Preventive, Restorative and Pediatric Dentistry,
School of Dental Medicine, University of Bern,
Bern, Switzerland
e-mail: [email protected]
U. Bringolf
Nordstrasse 26,
8200 Schaffhausen, Switzerland
throughout life. Visual deficiencies can be compensated for
with optical aids.
Clinical relevance Newly developed miniaturized vision
tests have allowed, in a clinically relevant way, to evaluate
the influence of magnification and age on the near visual
acuity of dentists.
Keywords Magnification systems . Dental loupes .
Operating microscope . Restorative dentistry . Presbyopia
Introduction
The use of optical aids to improve manual precision has
long been a tradition in many medical professions [1].
Dentistry seems to be an ideal environment for the use of
loupes and microscopes, because operative treatments are
performed in a small and narrow environment. However, the
idea that magnification devices should be used as standard
devices in dentistry is relatively new [2–4].
The body of evidence supporting the general assumption
that optical magnification improves the quality of caries
detection and filigree therapy is weak [5]. Most publications
about visual acuity and the influence of magnification [6–9],
or concerning microscopes and endodontics [2, 10–12], are
based on expert opinions and case reports. An obvious gap
between anecdotal conjecture and solid evidence-based decision making exists with respect to the use of optical aids in
dentistry.
In a previous study [5] with the help of miniaturized
visual tests and a light box, the present authors found a large
variability in the near visual acuity of dentists and a significant correlation with the dentists’ age. Yet, the tests were
not incorporated in an oral cavity, and thus, the clinical
relevance of these miniaturized visual tests was limited.
726
Therefore, the aims of the present study were:
1. To test near visual acuity and the influence of magnification and age in a simulated clinical situation
2. To compare the results to the previous study, where the
same group of dentists was tested under standardized
conditions ex ore with a light box
Materials and methods
The near visual acuity of 40 dentists from the Dental School
of the University of Bern was evaluated using miniaturized
visual tests fixed in a dental phantom head unit. The distribution of the dentists in the different age groups was as follows:
25–30 years, n016; 31–35 years, n09; 36–40 years, n02; 41–
45 years, n05; 46–50 years, n01; 51–55 years, n03; 56–
60 years, n03; 61–65 years, n01.
Visual tests with E-optotypes, ranging from 0.05 to
0.5 mm, allowed for the quantification of visual acuity at a
typical dental working distance, as described in a previous
study [5]. The tests were mounted in cavities in maxillary
second premolars and first molars of a dental phantom unit
(KaVo, Biberach, Germany) (Fig. 1).
The head was positioned on a dental chair. Dental mirrors
(Rhodium Nr. 4, Hahnenkratt GmbH, Königsbach,
Germany) were used, and the operating lamp (Delight,
Planmeca OY, Helsinki, Finland) for conditions 1 through
4 was individually arranged by the test persons.
Fig.1 The fixation of the visual tests in distal box cavities of phantom
teeth allows the testing of visual acuity under simulated clinical
conditions
Clin Oral Invest (2013) 17:725–729
Visual performance was tested under the following
conditions:
1. Natural visual acuity (NV): no magnification devices,
distance of 300 mm (typical working distance), operating lamp
2. Free natural visual acuity (NVf): no magnification devices and free choice of the distance (typical controlling
distance), operating lamp
3. Galilean loupe system (G) (EVC250N, SurgiTel, Ann
Arbor, MI, USA): magnification of ×2.5; distance of
380 mm; operating lamp
4. Keplerian loupe system (K) (EyeMag Pro S, Zeiss,
Oberkochen, Germany): magnification of ×4.3; distance
of 400 mm; operating lamp
5. Operating microscope (M4×) (Leica M300, Leica
Microsystems, Heerbrugg, Switzerland): magnification
of ×4; distance of 250 mm; integrated light
6. Operating microscope (M6.4×): same as condition 5,
but with magnification of ×6.4.
The loupes were fixed on a headband, which allowed the
dentists to wear their respective prescription eyeglasses
(when necessary) in all groups. During the visual tests, the
position of the loupes, the eye–object distance, and the
reading of the E-optotypes were all controlled by the same
expert. The smallest line of the visual test that could be read
without mistakes was registered.
The distance between the three bars of the letter E (01/5
the size of E) corresponds to the smallest detectable structure [13] and allows to calculate the visual acuity. The
metric dimension of the bar spacing in the registered line
(e.g., 0.03 mm) was converted into the reciprocal value
(e.g., 33.3/mm). This allowed to achieve a positive correlation between the metric value and the quality of the visual
performance. The influence of the different magnification
systems (conditions 1–6) was tested for all dentists. To investigate the influence of the dentists’ age, the present authors
calculated the correlation between age and visual acuity for
the different optical conditions and compared the results of the
two subgroups A <40 years (n027) and B ≥40 years (n013).
Finally, the results of the present study were compared with
the results of the previous study, where the visual performance
of the same dentists was tested on the light box and not in a
setup simulating the clinical situation.
For statistical analysis, the software R version 2.13.0
(www.r-project.org) was used. The significance level was
set at α00.05. Descriptive statistical analysis was carried
out to determine the means and medians as well as the
nonparametric 95 % confidence intervals (CI) for all dentists. The influence of the respective groups of dentists and
different loupe systems on the visual acuity was analyzed by
using rank tests for linear models based on Wilcoxon scores
[14], followed by Wilcoxon signed rank tests with
Clin Oral Invest (2013) 17:725–729
727
Bonferroni–Holm correction for multiple comparisons as
post hoc tests. Spearman’s rank correlation coefficient was
used to detect monotone relationships between age and
visual acuity. For the third part, Spearman’s rank correlation
coefficient and Pearson’s correlation coefficient were used
to detect monotone and linear relationships between the
results of the previous study and those of the present one
concerning NV, G, and K.
Table 2 The correlation between age and visual performance was medium for all
optical conditions except NVf
(strong correlation) and
M6.4× (weak correlation)
Condition
Spearman’s rank
correlation
NV
−0.543
NVf
G
K
M4×
M6.4×
−0.747
−0.686
−0.563
−0.485
−0.286
Results
The mean visual performance of the tested devices is presented in Table 1. The relative improvement of visual performance with magnification ranged from 250 % (Galilean
loupe) to 961 % (operating microscope, ×6.4), compared to
natural visual acuity. Statistical analysis revealed significant
differences between all tested conditions (p<0.01) (Table 1).
The correlation between age and visual performance under
the different conditions is presented in Table 2. Spearman’s
rank correlation shows medium correlation values for most of
the conditions. The exceptions were NVf with a strong correlation and M6.4× with a weak correlation.
The mean visual performance, medians, and 95 % CIs for
groups A (<40 years) and B (≥40 years) are presented in
Table 3. For all tested conditions, significant differences
between the two groups were detected (p<0.001 or p<
0.05). Both groups benefitted from the magnification of
the Galilean and Keplerian loupes and even more from the
sophisticated optics of the operating microscope. The visual
acuity of group A in natural vision at a closer distance (NVf)
was better than the acuity of group B with Galilean loupes
(G). The difference between conditions NVf and G was not
as pronounced for group A as for group B.
Table 1 Visual performance (mean, median, nonparametric 95 %
confidence intervals) and the relative improvement of all tested dentists
under all test conditions
Condition
(1/mm)
NV*
NVf*
G*
K*
M4×*
M6.4×*
Mean
(1/mm)
Median
(1/mm)
8.43
15.20
21.07
31.94
57.27
81.01
11.52
18.04
21.01
34.34
53.48
81.59
95 % CI
(1/mm)
Improvement of
visual performance
(NV0100 %)
11.52–13.98
16.79–21.01
19.52–22.90
29.76–34.34
53.48–58.19
75.13–87.41
100
180
250
379
679
961
%
%
%
%
%
%
Note the difference between NV and NVf due to the natural magnification by moving closer to the object
*p<0.01, significant differences within the columns
The comparison of the present study with the previous
study on a light box [5] revealed a strong correlation between
the two setups when no magnification device was used (NV;
Spearman’s correlation coefficient, 0.698) and when the
Galilean system was used (G; Pearson’s correlation coefficient, 0.725). The correlation was medium for the Keplerian
system (K; Spearman’s correlation coefficient, 0.622).
Discussion
A large variability in natural visual acuity was found (0–
18.04, 1/mm bar spacing), which corroborated the results of
a previous study under optimal conditions ex ore [5]. Some
of the tested dentists had better visual acuity without optical
aids than others with Galilean loupes. The visual acuity can,
as expected, be significantly improved by the use of magnification devices (250–961 %, Table 1), independent of age
and natural visual acuity. When using Keplerian loupes, all
dentists achieved a significantly higher visual acuity than
with Galilean loupes. This could be expected due to the
magnification factor. The different magnification factors of
the two systems have a clinical rationale: Galilean loupes are
small and ergonomic but have a magnification limit of ×2.5
(×3.2 with optical constraints), while the magnification of
Keplerian loupes is not constrained. Keplerian loupes therefore provide an advantage at a magnification of ×3.5 and
above only.
The large difference between the microscope and the
head-mounted loupe systems, even with comparable magnification factors, was unexpected. The highly superior performance of the operating microscope could be due to the
different optical construction of the microscope with a greater angle between the two optical beams. A further, possibly
even more important reason could be the static position of
the microscope, which offsets any disturbances caused by
head movements. This effect is only detectable in a simulated clinical setting as used in this study.
Presbyopia (loss of accommodation) starts around the age
of 40 years and is combined with other changes in the eye,
such as decreasing sensitivity to contrast, increasing sensitivity
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Clin Oral Invest (2013) 17:725–729
Table 3 Visual performance (mean, median, nonparametric 95 % confidence intervals) for the two groups <40 and ≥40 years under all test
conditions
Condition
NV*
NVf*
G*
K*
M4×**
M6.4×**
Age ≥40 years (n013) (1/mm)
Age <40 years (n027) (1/mm)
Mean
Median
11.16
20.29
23.38
34.38
60.07
85.15
11.52
21.01
21.01
34.34
58.19
87.41
95 % CI
Mean
Median
11.52–14.63
18.27–21.01
21.01–25.38
32.05–37.01
55.49–64.61
82.59–94.21
3.35
5.75
16.78
27.39
52.06
73.31
0
0
18.04
27.28
48.08
75.76
95 % CI
n.a.
n.a.
14.78–18.04
24.80–29.76
48.08–55.49
62.84–81.59
Note the differences from NVf to G between the two groups
n.a. Not available: due to the skewed distribution, a calculation of the 95 % confidence interval was not possible (in the older group when visual
performance with the naked eye was tested
*p<0.001; **p<0.05, significant differences within the columns
to glare, and lower visual performance [15, 16]. The influence
of presbyopia on the visual performance was analyzed in two
different mathematical approaches. Spearman’s rank correlation confirmed a decrease in the visual acuity over time. The
strong correlation between age and natural visual acuity in a
free, i.e., closer, distance (NVf) could be expected due to the
loss of accommodation. However, the only marginal correlation between age and acuity using the microscope (M6.4×) was
unexpected. An explanation could be the fact that the microscope allows a parallel view without any accommodation and
is therefore less able to account for presbyopic deficiencies.
The division into two groups (<40 and ≥40 years old)
allowed the quantification of the age-related deficiencies in a
second, more comprehensible approach. The decrease in visual
performance is important. In the group ≥40 years old, the
condition NVf exhibited a 72 % lower visual performance.
This condition has an evident clinical importance: by reducing
the working distance, the dentist profits from a natural magnification which is quantified in the difference between the conditions NV and NVf in the younger group A (<40 years old)
(Table 3). This natural magnification is widely used in diagnostic situations and mostly compromised with increasing age.
The comparison of the extraoral visual test under optimum
visual conditions (direct view, light box, supported head) with
the intraoral visual test in a phantom head showed a strong
correlation for unaided natural vision and Galilean loupes.
The correlation for Keplerian loupes was less pronounced.
This could indicate that head-mounted higher magnifications
are more sensitive to tremors arising from the head and dental
mirrors in a clinical situation. However, an extraoral near
vision test seems to be a valid surrogate to judge the performance that would be achieved in the clinical situation.
Common near vision tests, such as those used by opticians, are physically too large to assess visual acuity at the
scale on which dentists work [5]. This is, with one exception
[17], also true for the few research studies identified in the
literature [15, 18, 19]. The E-optotypes used in the present
study ranged from 0.05 to 0.5 mm and were proven to have
adequate discriminatory properties [5]. The placement of the
tests in artificial teeth provided a realistic simulation of the
dental setting, including variables such as the illumination
source and the reduced contrast in a cavity, which may
influence the visual performance during dental work.
The most objective value for visual performance is the
visual acuity angle [13]. However, not all parameters for an
objective optical value can be standardized in a simulated
clinical setting. The pragmatic question of whether a small
structure can be recognized or not seems to be more adequate for a clinical approach. Therefore, the visual acuity
angle was substituted for the metric dimension of the smallest recognized bar spacing under the given conditions. The
reciprocal calculation of bar spacing allowed for a positive
correlation between metric values and visual performance.
The results of this study suggest the importance of reliable near vision tests for dental personnel. Dental students
as well as dental personnel with increasing age should be
aware of their natural near vision in order to choose adequate optical aids. This also holds true for other medical
branches. Whether or not an adjusted visual acuity has an
impact on the precision of diagnostic and operative procedures remains the subject of further studies.
Conclusion
The near visual acuity under simulated clinical conditions
varies highly between individuals and decreases over one’s
lifetime. This decrease is most pronounced in natural vision
without magnification devices. There is a need for a free
accessible visual test at a dental working distance to objectively
measure the visual performance of dental students and dental
personnel in order to provide personalized recommendations
Clin Oral Invest (2013) 17:725–729
for the use of magnification devices. Individuals with poor
natural visual acuity or an age ≥40 years can reliably compensate their visual deficiencies by using optical aids.
Acknowledgments The authors would like to acknowledge Philippe
Ducreux (Lunea-Group, France), Prof. Dr.-Ing. Andreas Ettemeyer
(NTB Interstaatliche Hochschule für Technik Buchs, Buchs, Switzerland), Martin Roost (Roost-Optik, Schaffhausen, Switzerland), and
René Seiler (Fischer & Loeliger Optik, Bern, Switzerland) for their
support with optical issues. The authors also thank Stefanie Hayoz
(Institute of Mathematical Statistics and Actuarial Science, University
of Bern, Switzerland) for the statistical analysis.
Conflict of interest The authors declare that they have no conflict of
interest.
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